Proper operation of an ink jet printer requires parameters such as pressure, charging voltage, deflection voltage, stimulation amplitude and charge phase to be properly set. The appropriate value for each of these operational parameters will depend on several items. Because of differences in ink properties such as viscosity and surface tension, the optimal point for these operational parameters will vary from ink type to ink type. As the fluid properties of the ink are temperature dependent, the optimal setting for these operational parameters are also temperature dependent. Different ink will have different temperature dependencies as a result of its composition.
During operation of the printer, the concentration of the ink can changes. As the concentration of the ink drifts, the optimal point of the operational parameters will also shift. If left uncorrected, the changing concentration of the ink can make the ink jet printer not operable. Rather than allow this to occur, ink jet printers typically include some means to monitor the ink concentration. If the concentration of the ink rises due to evaporation, the printer controls system will take corrective action by adding a replenishment fluid to drive the ink concentration back to the concentration set point. Means used to monitor the concentration include measurements of viscosity, resistivity or optical absorbance. Different inks will have different values for measured parameters at the desired concentration set point.
The operational parameters for the printer will depend on the characteristics of the printhead. For example, printheads with larger than nominal orifices might require slightly different pressures, charge voltage, and stimulation amplitude than printheads with smaller orifices.
Typical prior art systems could not self-configure themselves to properly set each of the operational parameters. Instead, the operator had to set various of these parameters. For example, the operator might have been given a printed list of parameters to set when changing a printhead. In other cases, these parameters would have to be determined experimentally, either manually by the operator or by a diagnostic test carried out by the printer, after installing a printhead. Changes in ink type either required the inks to operate at the same conditions or the new conditions had to be determined experimentally. No means was provided to deal with different temperature dependence characteristic for different ink. Differences in the measurement parameter for the concentration control from one ink type to another was also not dealt with.
In addition to the issue of operational parameters, different ink or printheads might require changes in the startup or shutdown sequences for optimal reliability. In continuous ink jet printing systems, it is necessary to execute a sequence of states in order to effectively perform operations of the systems. A particular sequence is used, for example, to bring the printhead to a ready-to-print condition. Another is used to shut down the printhead. And another is used to clean the printhead.
A state describes the physical configuration of the system, including valve positions, vacuum and ink pump operation, heater operation, and whether certain evolutions are enabled (ink fill, for example). The sequences and states are stored in processor memory in files known as state tables. Different state tables may be used for different inks.
U.S. patent application Ser. No. 08/810,653 now abandoned has provided a means for dealing with the issues of operational parameters, different ink or printheads which can require changes in the startup or shutdown sequences for optimal reliability. That application describes a system which is supplied with an index of available inks. For each ink type, setup values for each operation parameter are given. The temperature dependence of various of these parameters are also given. Furthermore, set points for the measured parameter of the concentration control are given. The control computer inputs a file with printer related characteristics. These might include values related to the measurement system used for concentration control. For example, in a resistivity measurement cell for concentration, small changes in the spacings of the electrodes might produce a shift in the measured voltage or current from the cell at the desired set point. Such a correction or parameter might be included in the printer configuration files. Other values in the printer configuration files might include revision level of hardware or software information which might affect setup.
Additional input files for the computer can include printhead related values. These values can provide a means to correct or account for manufacturing tolerance related shifts in the operating parameters. Such values might be supplied directly from a memory unit built into the printhead, or by means of an externally supplied file, on a floppy disk for example.
Application Ser. No. 08/810,653 now abandoned provides an efficient manner to store and utilize this information in the form of tables or matrix arrays. For example, each step in a start up sequence can be stored as a matrix of values, where each location in the matrix corresponds to status of a particular valve, pump or other component. The whole start up sequence then corresponds to an array identifying the order of such steps. Values of the various operating parameters as determined by the various input files are either inserted directly or combined appropriately and then inserted into the appropriate control matrix locations. For example if ink XXX is installed, the data from the ink characteristic matrix appropriate for ink XXX is accessed and inserted into the appropriate printer control matrix. From the same ink characteristic matrix, temperature compensation parameters are retrieved to modify the control equations. A different sequence of startup steps might also be called out by the data from the ink characteristic matrix.
In application Ser. No. 08/810,653, now abandoned states were executed sequentially within a sequence. Most states were executed for a finite length of time. A few states, such as end of sequence states, had no defined operating time. The printer would remain in the state until the operator called for a change of sequence or to progress to the next state in the sequence.
While this provided an efficient means to configure the printer to properly set the various operating parameters and control sequences in response to differing printhead, ink and fluid system component characteristics, it also had significant limitations. For example, if one desired for the system to pause in a particular state until the system warmed up to a threshold temperature, there was no method to do so except to guess the length of time that it might take to reach that temperature. Thus, sometimes the system might remain in the state longer than necessary. This could result in unnecessary delay in restarting the printer. Other times, the system might exit the state without reaching the temperature threshold. This might produce an ink jet related error which would require the printhead to be restarted from the first state in the startup sequence. The effect would be a lower apparent reliability for the printer and a prolonged startup sequence.
Therefore, it would be desirable to have an improved method for control of sequencing of states in an ink jet printing system, which maintains self configuring characteristics while providing more flexibility to control of state sequencing.